1. Field of the Invention
The present invention relates to an interdomain routing system and, more particularly, to a routing system (device) enabling path selection taking network resources into consideration end to end by using, at a node in a certain domain, path information in other domain to which no routing information is notified.
2. Description of the Related Art
One example of an interdomain QoS routing system as a conventional interdomain routing system is recited in the proposal by B. Abarbanel, entitled “BGP-4 Support for Traffic Engineering”, pages 1 through 13 of draft-abarbanel-idr-bgp4-te-01.txt which was issued as an Internet draft of IETF in 2000.
The conventional interdomain QoS routing system is a system (BGP-TE system) which realizes routing in consideration of load distribution or QoS (quality of service) by adding new link metrics such as a residual bandwidth and a delay to a border gateway protocol (BGP) to control routing between autonomous system (AS) domains so as to optimize these link metrics.
The link metrics are assigned to roughly two kinds of links, a link between AS and a link for relaying within an AS. As to a link between AS, parameters can be extracted from a residual bandwidth, a delay and the like of a physical link. As to information about a link between AS, path information is exchanged by an external BGP (E-BGP) session set between border routers of the AS.
On the other hand, in a case of a link relaying within an AS, parameters such as a residual bandwidth and a delay should be assigned to a logical link passing through a plurality of routers and a plurality of links existing in the AS. As to information about a logical link of relays in the AS, path information is exchanged by an internal BGP (I-BGP) session set up between AS border routers in the AS. The path of the I-BGP session will form a path of a logical link, and residual bandwidth and delay values on the path should be obtained and reflected on metrics of the logical link.
For this purpose, by extending an intradomain gateway protocol (IGP), for example, Open Shortest Path First (OSPF) or Integrated Intermediate System Intermediate System (integrated IS-IS) to employ a system (IGP-TE system) of exchanging parameters such as a residual bandwidth and a delay for a physical link, values of a residual bandwidth, a delay and the like on a path of the logical link can be obtained and notified to the I-BGP.
By the foregoing procedure, such metrics as a residual bandwidth and a delay can be added to each path of an E-BGP session between AS and an I-BGP session passing within an AS.
At the path selection from a terminal or a router in an AS-A to a terminal or a router in other AS-B in consideration of a residual bandwidth and a delay using both of the above-described conventional BGP-TE system and IGP-TE system, such path selection as follows is conducted. AS border router candidates which can be routed from a terminal or a router in the AS-A to the AS-B are extracted from IGP-TE information.
In a case where the OSPF is used as an IGP, for example, distribution of address reachability from an AS border router in the AS-A to an external AS by using an AS external LSA leads to recognition. In general, however, only with IGP-TE information, address reachability from an AS border router to an external AS can be recognized, while resource information can not be found about how much bandwidth, delay or the like is required to reach a certain external AS.
Here, as proposed in the BGP-TE system, when a terminal or a router in the AS-A operates the IGP-TE protocol, in particular, and an I-BGP session is set between the terminal or router and an AS border router in the AS-A to enable reception of BGP-TE protocol information, since a candidate for a path from an AS border router candidate in the AS-A to the AS-B can be extracted from the BGP-TE information, selection of an optimum path to reach from a terminal or a router in the AS-A to the AS-B through a border router in the AS-A taking a residual bandwidth and a delay into consideration is enabled by conducting path calculation together with IGP-TE information.
Although this path selection is possible from a terminal or a router in the AS-A to an AS border router in the AS-B, path selection from an AS border router in the AS-B as a final AS to a destination terminal or router in the AS-B is impossible. Further problem is that selection of an optimum AS border router to reach a destination terminal or a router in the AS-B in consideration of a result of the path selection in the AS-B is impossible.
In this problem, there might be a case where even when path selection, for example, from a terminal or a router in the AS-A to an AS border router in the AS-B is optimum, the path selection may result in being not optimum in the end-to-end view because a path from an AS border router in the AS-B to a destination terminal or router in the AS-B congests and there remains only a path having few residual bandwidths and a large delay. Conventional techniques therefore have the problem that when interdomain QoS routing is conducted, optimum path selection covering the entire path (end-to-end) is impossible.
Another example of a conventional interdomain routing system (not an interdomain QoS routing system) will be described as a related and similar technique. One example of a device of this kind is recited in the technical explanatory by K. Delgadillo, entitled “Cisco Distributed Director” on pages 1 through 19 of the white paper issued by Cisco Systems Inc. in 1999.
The technique disclosed in the explanatory is proposed as a Web load distribution system in which when a Web client accesses a Web server, on the assumption that a plurality of Web mirror servers exist in a network, a path is selected which employs a Web server of a low processing load and as short a path of a network as possible. Under Web environments, conducted is transaction processing in which an HTTP get request is made by the Web client side to a server and the Web server returns an HTTP response to the Web client side.
Since the amount of transferred information of an HTTP response is large in general, at the path selection, an optimum path from a Web server directed toward a Web client largely affects the performance. In other words, when a plurality of Web mirror servers exist, it is necessary to determine in total from which mirror server a path to the Web client is the shortest or which Web mirror server has a low processing load of its own.
In order to satisfy the above-described requirement, the present technique proposes a direct response protocol (DRP) by which a DRP agent of a Web client site can collect, for a DRP server existing in a plurality of Web mirror server sites, all of the shortest paths directed toward the Web client from the respective mirror servers and processing loads of the Web mirror servers, so that an optimum Web mirror server can be selected based on the collection result. Network assumed at this time is an interdomain network, in which a shortest path from a Web mirror server directed toward a Web client is obtained by acquiring information about both the number of hops of AS at the BGP (border gateway protocol) level and the number of hops of routers at the IGP (intradomain gateway protocol) level.
In other words, characteristic points are two, one is that a shortest path in interdomain routing is obtained by using information of both the BGP level and the IGP level and the other is that a system is adopted which takes a shortest path of a network in a reception direction into consideration in order to select a Web server with which a Web client is to communicate.
The DRP protocol, as well as the above-described BGP-TE, however, is not allowed to make end-to-end optimum path selection because selection of an optimum AS border router in the final stage AS and selection of a path from an AS border router to a Web client are not taken into consideration.
The above-described conventional interdomain routing has several problems. More specifically, the first problem is that path selection in an interdomain network is impossible which is conducted taking network resources such as a bandwidth and a delay into consideration end to end. The reason is that when only the conventional BGP-TE system and the IGP-TE system are used, while path selection in an AS on the transmission side and selection of a path from the transmission side AS to a destination AS can be conducted using network resources, selection of an optimum AS border router in the destination AS and selection of an optimum path from a selected AS border router to a destination terminal or router are impossible.
Second problem is that when path selection is conducted taking network resources such as a bandwidth and a delay into consideration end to end, an optimum path in a reception direction can not be selected. The reason when a DRP is used is that while a path in the reception direction can be returned, no optimization is made because path information of a transmission domain is not used in combination. The reason when only a BGP-TE and a IGP-TE are used is that because the BGP-TE, in particular, has information about a path only in the transmission direction, the selection of an optimum path only in the transmission direction is possible even using both the TE.
Third problem is that path selection is impossible that simultaneously satisfies an optimum server and an optimum network path therefor in consideration not only of QoS parameters such as a residual bandwidth and a delay of a network path but also of a load of a server. The reason is that no function is provided for notifying all of server load information, network path candidate information and QoS metric information.